diff --git a/src/vs/workbench/api/browser/mainThreadTesting.ts b/src/vs/workbench/api/browser/mainThreadTesting.ts
index 8bb2b187745..c2c8ac5805b 100644
--- a/src/vs/workbench/api/browser/mainThreadTesting.ts
+++ b/src/vs/workbench/api/browser/mainThreadTesting.ts
@@ -11,7 +11,7 @@ import { URI } from 'vs/base/common/uri';
 import { Range } from 'vs/editor/common/core/range';
 import { extHostNamedCustomer } from 'vs/workbench/api/common/extHostCustomers';
 import { MutableObservableValue } from 'vs/workbench/contrib/testing/common/observableValue';
-import { ExtensionRunTestsRequest, ITestItem, ITestMessage, ITestRunProfile, ITestRunTask, ResolvedTestRunRequest, TestDiffOpType, TestResultState, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
+import { ExtensionRunTestsRequest, ITestItem, ITestMessage, ITestRunProfile, ITestRunTask, ResolvedTestRunRequest, SerializedTestMessage, TestDiffOpType, TestResultState, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
 import { ITestProfileService } from 'vs/workbench/contrib/testing/common/testProfileService';
 import { TestCoverage } from 'vs/workbench/contrib/testing/common/testCoverage';
 import { LiveTestResult } from 'vs/workbench/contrib/testing/common/testResult';
@@ -176,7 +176,7 @@ export class MainThreadTesting extends Disposable implements MainThreadTestingSh
 	/**
 	 * @inheritdoc
 	 */
-	public $appendTestMessagesInRun(runId: string, taskId: string, testId: string, messages: ITestMessage[]): void {
+	public $appendTestMessagesInRun(runId: string, taskId: string, testId: string, messages: SerializedTestMessage[]): void {
 		const r = this.resultService.getResult(runId);
 		if (r && r instanceof LiveTestResult) {
 			for (const message of messages) {
@@ -185,7 +185,7 @@ export class MainThreadTesting extends Disposable implements MainThreadTestingSh
 					message.location.range = Range.lift(message.location.range);
 				}
 
-				r.appendMessage(testId, taskId, message);
+				r.appendMessage(testId, taskId, message as ITestMessage);
 			}
 		}
 	}
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index d8a28c2000d..e3e1eb4ced1 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -24,7 +24,6 @@ import { EndOfLineSequence, ISingleEditOperation } from 'vs/editor/common/model'
 import { IModelChangedEvent } from 'vs/editor/common/model/mirrorTextModel';
 import * as modes from 'vs/editor/common/modes';
 import { CharacterPair, CommentRule, EnterAction } from 'vs/editor/common/modes/languageConfiguration';
-import { ILanguageStatus } from 'vs/workbench/services/languageStatus/common/languageStatusService';
 import { IAccessibilityInformation } from 'vs/platform/accessibility/common/accessibility';
 import { ICommandHandlerDescription } from 'vs/platform/commands/common/commands';
 import { ConfigurationTarget, IConfigurationChange, IConfigurationData, IConfigurationOverrides } from 'vs/platform/configuration/common/configuration';
@@ -60,12 +59,13 @@ import { ICellRange } from 'vs/workbench/contrib/notebook/common/notebookRange';
 import { InputValidationType } from 'vs/workbench/contrib/scm/common/scm';
 import { ITextQueryBuilderOptions } from 'vs/workbench/contrib/search/common/queryBuilder';
 import { ISerializableEnvironmentVariableCollection } from 'vs/workbench/contrib/terminal/common/environmentVariable';
-import { CoverageDetails, ExtensionRunTestsRequest, IFileCoverage, ISerializedTestResults, ITestItem, ITestMessage, ITestRunProfile, ITestRunTask, ResolvedTestRunRequest, RunTestForControllerRequest, TestResultState, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
+import { CoverageDetails, ExtensionRunTestsRequest, IFileCoverage, ISerializedTestResults, ITestItem, ITestRunProfile, ITestRunTask, ResolvedTestRunRequest, RunTestForControllerRequest, SerializedTestMessage, TestResultState, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
 import { InternalTimelineOptions, Timeline, TimelineChangeEvent, TimelineOptions, TimelineProviderDescriptor } from 'vs/workbench/contrib/timeline/common/timeline';
 import { TypeHierarchyItem } from 'vs/workbench/contrib/typeHierarchy/common/typeHierarchy';
 import { EditorGroupColumn } from 'vs/workbench/services/editor/common/editorGroupColumn';
 import { ActivationKind, ExtensionHostKind, MissingExtensionDependency } from 'vs/workbench/services/extensions/common/extensions';
 import { createExtHostContextProxyIdentifier as createExtId, createMainContextProxyIdentifier as createMainId, IRPCProtocol, SerializableObjectWithBuffers } from 'vs/workbench/services/extensions/common/proxyIdentifier';
+import { ILanguageStatus } from 'vs/workbench/services/languageStatus/common/languageStatusService';
 import { CandidatePort } from 'vs/workbench/services/remote/common/remoteExplorerService';
 import * as search from 'vs/workbench/services/search/common/search';
 
@@ -2161,7 +2161,7 @@ export interface MainThreadTestingShape {
 	/** Updates the state of a test run in the given run. */
 	$updateTestStateInRun(runId: string, taskId: string, testId: string, state: TestResultState, duration?: number): void;
 	/** Appends a message to a test in the run. */
-	$appendTestMessagesInRun(runId: string, taskId: string, testId: string, messages: ITestMessage[]): void;
+	$appendTestMessagesInRun(runId: string, taskId: string, testId: string, messages: SerializedTestMessage[]): void;
 	/** Appends raw output to the test run.. */
 	$appendOutputToRun(runId: string, taskId: string, output: VSBuffer, location?: ILocationDto, testId?: string): void;
 	/** Triggered when coverage is added to test results. */
diff --git a/src/vs/workbench/api/common/extHostTesting.ts b/src/vs/workbench/api/common/extHostTesting.ts
index a1c85f54bf3..650d3947320 100644
--- a/src/vs/workbench/api/common/extHostTesting.ts
+++ b/src/vs/workbench/api/common/extHostTesting.ts
@@ -14,7 +14,7 @@ import { MarshalledId } from 'vs/base/common/marshalling';
 import { deepFreeze } from 'vs/base/common/objects';
 import { isDefined } from 'vs/base/common/types';
 import { generateUuid } from 'vs/base/common/uuid';
-import { ExtHostTestingShape, MainContext, MainThreadTestingShape } from 'vs/workbench/api/common/extHost.protocol';
+import { ExtHostTestingShape, ILocationDto, MainContext, MainThreadTestingShape } from 'vs/workbench/api/common/extHost.protocol';
 import { ExtHostCommands } from 'vs/workbench/api/common/extHostCommands';
 import { IExtHostRpcService } from 'vs/workbench/api/common/extHostRpcService';
 import { InvalidTestItemError, TestItemImpl, TestItemRootImpl } from 'vs/workbench/api/common/extHostTestingPrivateApi';
@@ -340,6 +340,21 @@ class TestRunTracker extends Disposable {
 				fn(test, ...args);
 			};
 
+		const appendMessages = (test: vscode.TestItem, messages: vscode.TestMessage | readonly vscode.TestMessage[]) => {
+			const converted = messages instanceof Array
+				? messages.map(Convert.TestMessage.from)
+				: [Convert.TestMessage.from(messages)];
+
+			if (test.uri && test.range) {
+				const defaultLocation: ILocationDto = { range: Convert.Range.from(test.range), uri: test.uri };
+				for (const message of converted) {
+					message.location = message.location || defaultLocation;
+				}
+			}
+
+			this.proxy.$appendTestMessagesInRun(runId, taskId, TestId.fromExtHostTestItem(test, ctrlId).toString(), converted);
+		};
+
 		let ended = false;
 		const run: vscode.TestRun = {
 			isPersisted: this.dto.isPersisted,
@@ -362,13 +377,11 @@ class TestRunTracker extends Disposable {
 				this.proxy.$updateTestStateInRun(runId, taskId, TestId.fromExtHostTestItem(test, ctrlId).toString(), TestResultState.Running);
 			}),
 			errored: guardTestMutation((test, messages, duration) => {
-				this.proxy.$appendTestMessagesInRun(runId, taskId, TestId.fromExtHostTestItem(test, ctrlId).toString(),
-					messages instanceof Array ? messages.map(Convert.TestMessage.from) : [Convert.TestMessage.from(messages)]);
+				appendMessages(test, messages);
 				this.proxy.$updateTestStateInRun(runId, taskId, TestId.fromExtHostTestItem(test, ctrlId).toString(), TestResultState.Errored, duration);
 			}),
 			failed: guardTestMutation((test, messages, duration) => {
-				this.proxy.$appendTestMessagesInRun(runId, taskId, TestId.fromExtHostTestItem(test, ctrlId).toString(),
-					messages instanceof Array ? messages.map(Convert.TestMessage.from) : [Convert.TestMessage.from(messages)]);
+				appendMessages(test, messages);
 				this.proxy.$updateTestStateInRun(runId, taskId, TestId.fromExtHostTestItem(test, ctrlId).toString(), TestResultState.Failed, duration);
 			}),
 			passed: guardTestMutation((test, duration) => {
diff --git a/src/vs/workbench/api/common/extHostTypeConverters.ts b/src/vs/workbench/api/common/extHostTypeConverters.ts
index f10a80a7bc7..549ed7ceea1 100644
--- a/src/vs/workbench/api/common/extHostTypeConverters.ts
+++ b/src/vs/workbench/api/common/extHostTypeConverters.ts
@@ -32,7 +32,7 @@ import { SaveReason } from 'vs/workbench/common/editor';
 import * as notebooks from 'vs/workbench/contrib/notebook/common/notebookCommon';
 import { ICellRange } from 'vs/workbench/contrib/notebook/common/notebookRange';
 import * as search from 'vs/workbench/contrib/search/common/search';
-import { CoverageDetails, DetailType, ICoveredCount, IFileCoverage, ISerializedTestResults, ITestErrorMessage, ITestItem, ITestItemContext, ITestTag, SerializedTestResultItem, TestMessageType } from 'vs/workbench/contrib/testing/common/testCollection';
+import { CoverageDetails, DetailType, ICoveredCount, IFileCoverage, ISerializedTestResults, ITestErrorMessage, ITestItem, ITestItemContext, ITestTag, SerializedTestErrorMessage, SerializedTestResultItem, TestMessageType } from 'vs/workbench/contrib/testing/common/testCollection';
 import { TestId } from 'vs/workbench/contrib/testing/common/testId';
 import { EditorGroupColumn } from 'vs/workbench/services/editor/common/editorGroupColumn';
 import { ACTIVE_GROUP, SIDE_GROUP } from 'vs/workbench/services/editor/common/editorService';
@@ -1640,7 +1640,7 @@ export namespace NotebookRendererScript {
 }
 
 export namespace TestMessage {
-	export function from(message: vscode.TestMessage): ITestErrorMessage {
+	export function from(message: vscode.TestMessage): SerializedTestErrorMessage {
 		return {
 			message: MarkdownString.fromStrict(message.message) || '',
 			type: TestMessageType.Error,
@@ -1650,10 +1650,11 @@ export namespace TestMessage {
 		};
 	}
 
-	export function to(item: ITestErrorMessage): vscode.TestMessage {
+	export function to(item: SerializedTestErrorMessage): vscode.TestMessage {
 		const message = new types.TestMessage(typeof item.message === 'string' ? item.message : MarkdownString.to(item.message));
 		message.actualOutput = item.actual;
 		message.expectedOutput = item.expected;
+		message.location = item.location ? location.to(item.location) : undefined;
 		return message;
 	}
 }
diff --git a/src/vs/workbench/api/common/extHostTypes.ts b/src/vs/workbench/api/common/extHostTypes.ts
index d36356e7b79..d4c3cf082a6 100644
--- a/src/vs/workbench/api/common/extHostTypes.ts
+++ b/src/vs/workbench/api/common/extHostTypes.ts
@@ -3324,6 +3324,7 @@ export class TestRunRequest implements vscode.TestRunRequest {
 export class TestMessage implements vscode.TestMessage {
 	public expectedOutput?: string;
 	public actualOutput?: string;
+	public location?: vscode.Location;
 
 	public static diff(message: string | vscode.MarkdownString, expected: string, actual: string) {
 		const msg = new TestMessage(message);
diff --git a/src/vs/workbench/contrib/testing/common/testCollection.ts b/src/vs/workbench/contrib/testing/common/testCollection.ts
index c7bc238a79b..d1666daeab0 100644
--- a/src/vs/workbench/contrib/testing/common/testCollection.ts
+++ b/src/vs/workbench/contrib/testing/common/testCollection.ts
@@ -8,6 +8,7 @@ import { MarshalledId } from 'vs/base/common/marshalling';
 import { URI } from 'vs/base/common/uri';
 import { IPosition } from 'vs/editor/common/core/position';
 import { IRange, Range } from 'vs/editor/common/core/range';
+import { ILocationDto } from 'vs/workbench/api/common/extHost.protocol';
 
 export const enum TestResultState {
 	Unset = 0,
@@ -109,6 +110,8 @@ export interface ITestErrorMessage {
 	location: IRichLocation | undefined;
 }
 
+export type SerializedTestErrorMessage = Omit<ITestErrorMessage, 'location'> & { location?: ILocationDto };
+
 export interface ITestOutputMessage {
 	message: string;
 	type: TestMessageType.Info;
@@ -116,6 +119,10 @@ export interface ITestOutputMessage {
 	location: IRichLocation | undefined;
 }
 
+export type SerializedTestOutputMessage = Omit<ITestOutputMessage, 'location'> & { location?: ILocationDto };
+
+export type SerializedTestMessage = SerializedTestErrorMessage | SerializedTestOutputMessage;
+
 export type ITestMessage = ITestErrorMessage | ITestOutputMessage;
 
 export interface ITestTaskState {
diff --git a/src/vs/workbench/test/browser/api/extHostTesting.test.ts b/src/vs/workbench/test/browser/api/extHostTesting.test.ts
index de080ec74a8..f1d4fe47020 100644
--- a/src/vs/workbench/test/browser/api/extHostTesting.test.ts
+++ b/src/vs/workbench/test/browser/api/extHostTesting.test.ts
@@ -11,11 +11,12 @@ import { mockObject, MockObject } from 'vs/base/test/common/mock';
 import { MainThreadTestingShape } from 'vs/workbench/api/common/extHost.protocol';
 import { TestRunCoordinator, TestRunDto, TestRunProfileImpl } from 'vs/workbench/api/common/extHostTesting';
 import * as convert from 'vs/workbench/api/common/extHostTypeConverters';
-import { TestMessage, TestResultState, TestRunProfileKind, TestTag } from 'vs/workbench/api/common/extHostTypes';
-import { TestDiffOpType, TestItemExpandState } from 'vs/workbench/contrib/testing/common/testCollection';
+import { TestMessage, TestResultState, TestRunProfileKind, TestTag, Location, Position, Range } from 'vs/workbench/api/common/extHostTypes';
+import { TestDiffOpType, TestItemExpandState, TestMessageType } from 'vs/workbench/contrib/testing/common/testCollection';
 import { TestId } from 'vs/workbench/contrib/testing/common/testId';
 import { TestItemImpl, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
 import { TestSingleUseCollection } from 'vs/workbench/contrib/testing/test/common/ownedTestCollection';
+import { URI } from 'vs/workbench/workbench.web.api';
 import type { TestItem, TestRunRequest } from 'vscode';
 
 const simplify = (item: TestItem) => ({
@@ -572,6 +573,47 @@ suite('ExtHost Testing', () => {
 			assert.deepStrictEqual(proxy.$addTestsToRun.args, expectedArgs);
 		});
 
+		test('adds test messages to run', () => {
+			const test1 = new TestItemImpl('ctrlId', 'id-c', 'test c', URI.file('/testc.txt'));
+			const test2 = new TestItemImpl('ctrlId', 'id-d', 'test d', URI.file('/testd.txt'));
+			test1.range = test2.range = new Range(new Position(0, 0), new Position(1, 0));
+			single.root.children.replace([test1, test2]);
+			const task = c.createTestRun('ctrlId', single, req, 'hello world', false);
+
+			const message1 = new TestMessage('some message');
+			message1.location = new Location(URI.file('/a.txt'), new Position(0, 0));
+			task.failed(test1, message1);
+
+			const args = proxy.$appendTestMessagesInRun.args[0];
+			assert.deepStrictEqual(proxy.$appendTestMessagesInRun.args[0], [
+				args[0],
+				args[1],
+				new TestId(['ctrlId', 'id-c']).toString(),
+				[{
+					message: 'some message',
+					type: TestMessageType.Error,
+					expected: undefined,
+					actual: undefined,
+					location: convert.location.from(message1.location)
+				}]
+			]);
+
+			// should use test location as default
+			task.failed(test2, new TestMessage('some message'));
+			assert.deepStrictEqual(proxy.$appendTestMessagesInRun.args[1], [
+				args[0],
+				args[1],
+				new TestId(['ctrlId', 'id-d']).toString(),
+				[{
+					message: 'some message',
+					type: TestMessageType.Error,
+					expected: undefined,
+					actual: undefined,
+					location: convert.location.from({ uri: test2.uri!, range: test2.range! }),
+				}]
+			]);
+		});
+
 		test('guards calls after runs are ended', () => {
 			const task = c.createTestRun('ctrl', single, req, 'hello world', false);
 			task.end();